When we use gpg to create new key pair as follow:

$ gpg --kengen

We sometimes see message as below:

We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
++++++++++++++++++++++++++++++.+++++.++++++++++.
++++++++++.++++++++++.++++++++++++++++++++++++++
++++..++++++++++.++++++++++++++++++++++++++++++...
...............>+++++..........................................................................
.........................................................................................+++++

Not enough random bytes available.  Please do some other work to give
the OS a chance to collect more entropy! (Need 284 more bytes)

Here are some methods to help you generate enough entropy:

• Use EGD.
• cat <large file> > /dev/null
• Buy a special hardware - True hardware random number generators.